Method for preventing activation of silica in ore flotation



United States Patent 3,382,976 METHOD FOR PREVENTING ACTIVATION OF SILICA IN ORE FLOTATION Vennncio Mercade, Metuchen,"N.J., assignor, by mesne assignments, to Engelhard Minerals & Chemicals Corporation, Edison, N.J., a corporation of Delaware No Drawing. Filed May 19, 1965, Ser. No. 457,182

7 Claims. (Cl. 209-467) ABSTRACT OF THE DISCLOSURE A small amount of a water-soluble ferrocyanide or ferricyanide salt is added to a flotation pulp in order to prevent activation of quartz by iron sols when the pulp is floated in the presence of a fatty acid collector.

This invention relates to ore beneficiation, especially to the beneficiation of ores containing silica or quartz gangue.

When silica minerals, such as quartz, are present in aqueous ore pulps which also contain soluble iron salts, the silica tends to become activated by the iron compounds. When an aqueous ore pulp containing the activated silica is conditioned for flotation beneficiation with collector reagents, such as higher fatty acids, the silica will tend to report in the froth concentrate along with the desired minerals. This will occur even when a conventional silica depressant, such as sodium silicate, is present. Washing of the ore pulp is helpful, especially when the iron is present as a ferrous salt, but it is usually not possible or practical to wash the ore to the extent that the silica is no longer activated. I have discovered that iron-activation is especially pronounced when conditions in the pulp result in hydrolysis of the iron salts, forming certain iron sols, especially ferric monohydrate sol.

As a result of hypothesizing as to the nature and mechanism of iron-activation of quartz, I have discovered a simple and highly effective method for depressing quartz in an aqueous ore pulp containing iron compounds which would normally activate the quartz, i.e., iron compounds that cause quartz to float when conditioned with collector reagents such as fatty acid reagents which normally do not collect silica.

Briefly stated, in accordance with the present invention, a water-soluble hexacyanoferrate, preferably potassium ferrocyanide, K.;(Fe(CN) is used to depress silica in an aqueous ore pulp containing soluble iron compounds. A very small quantity of the soluble complex coordination compound is incorporated with agitation into an aqueous ore pulp containing the silica. The ore pulp, thus treated, is then conditioned for froth flotation with flotation reagents, such as high fatty acids, which are sel ctive to a desired constituent of the ore. The silica, depressed as a result of the hexacyanoferrate treatment, reports in the flotation tailings, as desired.

It is believed that the depression of iron-activated silica is obtained by reversing the charge on the iron-containing sol adsorbed on the surface of the silica by means of the polyvalent complex, with especially noteworthy results being realized with the tetravalent ferrocyanide ion.

The present invention is applicable to the treatment of metallic ores, such as iron, tin, manganese, titanium, and chromite ores, containing silica or quartz gangue and also containing soluble ferrous and/ or ferric salts. The invention is especially applicable to the treatment of heavy metal oxide ore which is collected with the familiar anionic (higher fatty acid) collector reagents, such as tall oil acids, oleic acid, sulfo-oleic acid, lauric acid, etc.

3,382,976 Patented May 14, 1968 The water-soluble hexacyanoferrates can be hexacyanoferrates (II) or hexacyanoferrates (III). These materials are also referred to as alkali and alkaline earth metal salts of ,f-errocyanic or ferricyanic acid. I prefer to use the ferrocyanide salts, which contain the quadrivalent anion Fe(CN) Ferricyanide salts are similar in structure but contain the trivalent anion Fe(CN) Of the watersoluble ferrocyanides, I prefer to employ potassium ferrocyanide K (Fe(CN) because of its comparatively low cost and availability. Examples of other soluble ferrocyanides are ammonium ferrocyanide, sodium ferrocyanide and calcium ferrocyanide. The quantity of soluble hexacyanoferrate is usually within the range of 0.001 to 1 pound per ton of ore.

In putting the invention into practice, the ore is crushed and ground to flotation-size feed and pulped. In many cases it may be desirable to wash the pulp with water or dilute acid to remove partially soluble salts. The hexacyanoferrate reagent is dissolved in water and aqueous ferrocyanide solution is added with agitation to the ore pulp. This can be carried out at ambient temperature. The pulp is normally acid at this point of the process since soluble iron salts occur in ores of an acid nature. After the solution of hexacyanoferrate is mixed thoroughly with the ore pulp, normally activated Silica will be depressed. The ore pulp can then be conditioned for froth flotation of the metal oxides from the silica and siliceous material. When finely divided ores or ores containing slimes are being beneficiated, a dispersant is employed. As examples of dispersants may be mentioned soluble alkali metal silicates, ammonium or alkali metal carbonates, and mixtures thereof. Alkali metal silicates also have a depressing effect on silica (when the silica is not ironactivated). Collector reagent or reagents for the desired metal oxide minerals are then added. The pulp is aerated and a froth withdrawn. The froth product is a concentrate of metal oxide minerals and the silica and siliceous minerals are concentrated in the tailings. The froth may be cleaned one or more times, and/ or the middlings recirculated, as in conventional flotation procedures.

The following examples illustrate this invention in greater detail. It will be distinctly understood, however, that the invention is not limited to the flotation concentration of the specific oxidized metals illustrated since the benefits of the invention are realized in the treatment of a wide variety of ores containing iron-activated Silica. minerals.

EXAMPLE I The following experiment was carried out .to demonstrate the iron-activation of quartz and the depression of the quartz in the system by means of potassium ferrocyanide. In order to avoid complexities and uncontrollable variables inherent in the use of a natural ore pulp, a synthetic ore pulp was made up with substantially pure calcite and silica flour. The object of the test was to float the calcite from the silica flour with fatty acid collector reagents. Iron-activation was simulated by adding ferrous sulfate to the pulp and then adding hydrogen peroxide, thereby forming a ferric sol which activated the silica. The calcite collector employed was a mixture of crude tall oil acids and mineral oil solution of an oil-soluble petroleum sulfonate. It was found that in the absence of ferrocyanaide deactivation, 66.8% by weight of the silica flour was activated and floated. Because of the presence of silica in the froth, the CaCO grade of the froth product was only 18.3 when the silica was iron-activated. By treating the iron-activated pulp with a small amount of potassium ferrocyanide before conditioning the pulp for flotation with the calcite collector reagents, only 12.7% by weight of the silica floated. The CaCO grade of the resulting froth product was 54.1%. In other words, more 3 4 than five times as much silica was activated and floated as evidenced by the higher Sn grade and lower weight of when the pulp was not treated with a ferrocyanide. The the froth obtained with the ferro'cyanide treated pulp. details of the flotation tests are as follows. The details are as follows:

In synthesizing the ore pulp, 750 grams of silica flour Tin run-of-rnine ore from Bolivia was crushed until were blunged at 25% solids in distilled water. A 1% it was fine enough to pass through a 20-mesh screen. A aqueous solution of FeSO .7I-I O was added to the Water sample containing five hundred grams (dry bvasis) of the in amount of 128 milliliters, the amount being calculated crushed ore was wet screened through a 65-'mesh screen to provide 100 mg. Fe++ per liter of solution. The system and the plus 65-mesh material rod milled for three was agitated for 5 minutes. The pH was 6.0. Three milliminutes at 60% solids. Soft water was used in the rod liters of 5% sulfuric acid solution was added, bringing mill. The pH during grinding was the natural pH of the the pH to 3.7. Following this, 10 milliliters of 3% hydroore, i.e., about 3.5 to 4.0. All of the minus 65-mesh ore gen peroxide was added to promote hydrosol formation. was combined and soluble salts were removed by placing The pH was 3.4. In the test made with potassium ferrothe minus 65-mesh ore in a 4 liter beaker, allowing the cyanide reagent, 2.5 milliliters of a 1% aqueous solution solids to settle, decanting the liquid, adding soft water of potassium ferrocyanide K (Fe(CN) ).3H O was added to the solids until the beaker was substantially full and after peroxide addition, bringing the pH to 3,3, The decanting the liquid. The ore still contained soluble feramount of potassium ferrocyanide used corresponds t rous salt, as shown by qualitative analysis. Ten milliliters 0.067 pound K (Fe(CN) ).3H O per ton of silica. In the of a 1% aqueous solution of K (Fe(CN) -3H O were control test, no ferrocyanide was added after the addition added to the washed minus 65-mesh ore at 30% solids of peroxide and before conditioning the pulp for flotation go and the pulp was agitated for 5 minutes. The pH was of calcite. In conditioning the pulp for flotation of calcite, -4. The amount of ferrocyanide added corresponded to the pulp was alka-lized by adding 4.3 milliliters of a 10% Pound 4( )e) z p ton TheOre aqueous solution of odiu hydroxide and 112,5 grams f was then conditioned for froth flotation of the cassiterite al it wa added nd th pulp agitated fo n inut as follows. Fonty milliliters of a 5% aqueous solution of Forty-five milliliters of a 5% aqueous olution f sodium carbonate were added and conditioned for one monium sulfate were added and the pulp onditioned for minute. To this was added 40 milliliters of a 5% aqueous seconds. The pulp was then conditioned for five minsolution of 0 brand sodium silicate (about 38% solids utes with an aqueous emulsion containing 20 milliliters of and having 11 Percent 2 P z Weight basis of 2.5% aqueous ammonium hydroxide solution, and 137 The P Was than conditioned for 5 minllt$- drops (equivalent to 9.0 pounds per ton of silica) of a 30 one hundred and iwehty-hve drops 0f mixture mixture of equal weight proportions of crude tall oil acids mining equal P y Weight 0f Crude hall Oil acids and and Calcium Petronate. (Calcium Petronate is the Calcium n t Was added and conditioned for 30 trade name of a 50% solution of neutral iLg luble minutes. The pH W213 8.4. Addition Of 0.6 milliliter Of petroleum sulfonate in mineral oil.) The pH of the condiaqueous solution of sulfuric acid reduced the pH of tioned pulp was 8.6. The pulp was then conditioned for The Conditioned P p was Subjected to froth flotation 12 minutes with 127 drops of hydrocarbon oil (Eureka in a 500 gram Flow fiflta'tioh machine, removing M), equivalent to 8.0 pounds of oil per ton of silica. Single The pulp was subjected to froth floation in a 1000 The procedure was repeated without addition of potasgram Air l .11 the fr th refloatgd h times d sium ferrocyanide. The results are summarized in Table th f oth products o bin d, Th results are Summarized 40 II. The Sn values reported in this table were obtained by i T bl I, spectrochemioal analysis. The concentration efficiency TABLE IFEFFECT OF POTASSIUM FERROCYANIDF ON index used in this table is a value that is a measure of H FLOTATION or c ci'rE FROM rnoN. 0'r v both selectivity and recovery. This value is obtained by SILICA the following calculation:

Test Kgmewmotmzo, Concentration Efiicien'oy Index (0131) Lbsltm shca gsg gg gig Percent Sn (Froth Produet-Percent Sn (Head) Conc. (2.38-Percent Sn Head) X 5833 511556assessor: 5782? 3i? if? Dlstrbuhm Fmth Product Exampqe 2.38 is the maximum percent Sn that could be obtained in a froth product representing 20% of the total weight of This example demonstrates the application of the procthe ore and containing of the tin. The maxi-mum ess of this invention to the rougher benefication of a very concentration efliciency index would be 100.

TABLE IL-EFFE i FLo'ra'rIoN or bfsiri ihi'ih ifi dtifrt iiii driffff nti foii GANGUE R4(F0(CN)).3H2O, MIMI] Product iif ilt 33%? Lbs. ton Ore Percent Percent Percent Percent Sn (Galcu- Index Wt. Sn Sn Dist. Sn ted) iii? iii, 32:; 8:833 8:22 it? low grade (Bolivia) tin o-re containing iron activated I laim; The main P p Of the rougher flotation was to 1. In the flotation benefication of an acidic aqueous produce a preconcentrate containing about 20% of the ore pulp in the presence of a fatty acid collector reagent, weight of the ground ore and the highest possible grade said pulp containing silica and also containing ferric and recovery in terms of the tin values. The ore contained 7 O mono-hydrate sol resulting from the hydrolysis of an iron less than 0.5% Sn. In tests run with and without ferrocompound in said pulp, a method for depressing staid cyanide, cassiterite (SnO was floated with fatty acid silica so as to prevent activation and flotation of said silica reagents from gangue containing large amounts of silica as a result of the presence of said sol which comprises and silicate minerals. When the ferrocyanide reagent was incorporating an additive consisting essentially of a small used, less gangue reported with the cassiterite in the froth, 7;

amount of a water-soluble hexacyanoferrate salt into said ore pulp before subjecting said ore pulp to flotation in the presence of fatty acid collector reagent.

2. The method of claim 1 wherein said soluble hexacyan'oferrate salt is a ferrocyan-ide salt.

3. The method of claim 2 wherein said ferrocy anide salt is potassium ferrocyanide.

4. A method for heneficiating an aqueous acidic ore pulp containing silica and ferric monohydrate sol resulting from the hydrolysis .of soluble iron salt, which sol tends to activate said silica and cause it to float in the presence of a fatty acid collector reagent, said method comprising incorporating into said aqueous ore pulp an additive consisting essentially of a small amount of a soluble ferrocyanide salt, and thereafter adding fatty acid collector reagent selective to a desired constituent of said ore pulp, and subjecting the pulp to flotation benefica-tion.

5. The method of claim 4 in Which said ferrocyanide salt is potassium ferrocyanide.

6. A process for the froth flotation of a heavy meta oxide mineral from an aqueous acidic ore pulp containing quartz gangue and ferric monohydrate sol resulting from the hydrolysis of a soluble iron compound which comprises incorporating into said ore'pulp an additive consisting essentially of a small amount of potassium ferrocyanide, thereafter conditioning the pulp for selective flotation of said heavy metal oxide mineral with a fatty acid collector reagent and subjecting the pulp to froth flotation, producing a froth product which is a concentrate of said heavy metal oxide mineral and a tailing which is a concentrate of quartz.

7. The process of claim 6 in which said heavy metal oxide mineral is cassiterite.

References Cited UNITED STATES PATENTS 1,467,354 9/1923 Christensen 209167 1,950,537 3/1934 Bartho-lemy 209-167 2,106,800 2/1938 Fischer 209-167 2,399,845 5/1946 Allen 209167 FOREIGN PATENTS 77.57 1 5/1947 U.S.S.R.

HARRY B. THORNTON, Primary Examiner.

R. HALPER, Assistant Examiner. 

